1. Field of the Invention
This invention relates to an improved process for preparing fibers of aromatic polyamides whose chain extending bonds are coaxial or parallel and oppositely directed. The process relates primarily to application of cyclic tensioning forces to such fibers in the wet state before they have been dried.
2. Description of the Prior Art
Mol. Cryst. Liq. Cryst., 1987, Vol. 153, pp. 547-552, Roche et al. is concerned with macrostructural deformation of para-aramid fibers by application of tensile stresses to completely dried fibers and discloses a relationship between altered molecular macrostructure and modulus in dried fibers by application of a cycled stress.
Japanese Laid-Open Patent Application (Kokai) 60/17,113 naming Teijin as the applicant, discloses a process for hot drawing dry copolyamide fibers to as much as six times their original length at greater than 300.degree. C. It is, also, recommended that a preliminary single drawing of from 1.03-3.0X should take place on the wet fibers, before drying. It is said that such preliminary drawing causes individual filaments to remain separated from other filaments and to maintain their round cross section during the hot drawing. No cyclic drawing of never-dried fibers is suggested.
Japanese Laid-Open Patent Applications (Kokai) 85/88,117 and 86/167,015 and Japanese Patent Publications 80/11,764 and 80/11,763 all teach preparation of para-aramid fibers wherein there is a single drawing step applied to the fibers before drying. There is no suggestion that more than a single drawing step should be applied.